Common Paper Weights: LB To GSM Conversions

We often say that there’s no border to knowledge in the world, but the carrier of knowledge –paper is different.

When we need to custom-print a hardcover book, a booklet that promotes the company, or a personalized poster for a foreign company, we’re going to have a problem. I use “LB” to describe paper, but the other uses “GSM”. How should we convert paper weights?

Before answering this question, we need to know what “LB” and “GSM” first.

In China, the paper weight is called “gram weight”, it is commonly represented by GSM, meaning the grams per square meter of paper. But the United States and the United Kingdom adopt the British system and weigh paper in pounds (LB), it means the pounds per piece of paper.

And here are some formulas to be used,

• one ream paper = 500 piece paper
• one inch = 2.54cm
• one pound = 453.6g
• one GSM= the weight of one square meter of paper
• one LB= the weight of one ream paper = the weight of 500 pieces paper

Now we give an example with text paper. This paper is 25*38 inches. It is 25*0.0254*38*0.0254=0.6129 m², so the size of 500 pieces of paper is 500*0.6129 = 304.65m².

We assume that the weight of this paper is 1g per square meter. Then 500 pieces are 304.65 g; it is also 304.65/453.6 = 0.676 pounds. So for 25*38 inch text paper, 1 GSM = 0.676 LB

Make a conclusion, LB = GSM*length(m) * width(m) * 500 / 453.6

Is it a lot simpler? But it’s not over yet. From the above formula, we can see that the factor of the two units is related to the size of paper, but the size of paper varies in the world, so the conversion is also different. Next, I will focus on three kinds of common American paper.

Writing papers

Writing papers are generally used for letterhead and communication systems, but can also be used for advertising flyers printing, reports printing, or any other project where a lightweight paper is appropriate. The size of this paper is 17 *22 inch.

Text papers

Text papers are classified into offset paper or coated paper in China, it is typically used for the inside pages of book printing, brochure printing, and catalogue printing. The weight of text papers also lends itself to advertising flyers printing as well as letterhead and communication systems. The size of this paper is 25*38 inches.

Cover papers

Cover papers are also called C1S papers. It is heavier than text sheets and is generally used for the covers of hardcover book printing and folder printing where extra bulk and protection are needed. Other cover paper uses include calendar printing, menu printing, invitation and thanks cards printing.  The size of this paper is 20*36 inches.

The sizes of these three kinds of paper are different, so the factors of their LB and GSM are different. Is it a bit confusing? Don’t worry, I’ve listed a form for you.

Do you have any questions about the paper? Please contact us right now.